A vehicle, such as a hybrid vehicle, a plug-in hybrid vehicle, and an electric car, is provided with a high-voltage storage battery for power driving, an inverter device configured to perform power conversion. of a DC high voltage output of the high-voltage storage battery into an AC high voltage output and drive a motor, a DC-DC converter apparatus configured to convert the DC high voltage output of the high-voltage storage battery into a DC low voltage output and perform power supply to a low voltage load such as a light or a radio of the vehicle, and a low-voltage storage battery as an auxiliary power source of the low voltage load being mounted thereon.
In general, the DC-DC converter apparatus is provided with a high-voltage switching circuit which converts a DC high voltage into an AC. voltage, a transformer which insulates and converts the AC high voltage into an AC low voltage, low-voltage rectifier circuit which converts the AC low voltage into a DC voltage, and an output terminal which outputs the voltage-converted voltage. There is provided a DC-DC converter apparatus which adopts a metal case in order to dissipate heat generated by a plurality of switching elements configuring the high-voltage switching circuit and a plurality of rectifier elements configuring a constant-voltage rectifier circuit.
Such a DC-DC converter apparatus has a structure in which a transformer, a step-down circuit section, a step-up circuit. section, and a control circuit section are mounted onto an inner surface of the metal. case, and the step-down circuit section and the step-up circuit section are formed using a metal circuit board (for example, see paragraph [0018] of PTL 1)